Floyd Mayweather will meet Conor McGregor on Aug. 26 in arguably one of the biggest fights of all time if not the most lucrative matchup in combat sports history.

It's impossible to predict the revenue for a fight of this magnitude, but it's possible McGreogr's first professional boxing match will produce the most pay-per-view buys and live gate in history, which would topple Mayweather's previous records for his bout with Manny Pacquiao.

McGregor will lace up 10-ounce gloves as he steps into the ring with Mayweather as the current UFC champion looks to crossover from mixed martial arts into boxing for this huge showdown in Las Vegas.

While Mayweather vs. McGregor will certainly be the talk of the summer, this wasn't the first crossover fight to get headlines in the history of sports or entertainment. In fact, boxers have crossed over to mixed martial arts and even professional wrestlers have tried both sports in the past.

So let's take a look at the five most memorable crossover fights in history before Mayweather meets McGregor in August.

5

Tim Sylvia vs. Ray Mercer

In 2009, former UFC heavyweight champion Tim Sylvia decided to test himself in a mixed martial arts bout against "Merciless" Ray Mercer. Sylvia was best known as a knockout artist throughout his mixed martial arts career, but he was definitely at a disadvantage on the feet while throwing hands with Mercer, who was a former Olympic gold medalist and multi-time boxing champion as a heavyweight.

The fight only lasted one exchange as Sylvia threw a kick to the body before stepping into throw a punch, which was then countered by a vicious right hand from Mercer. Sylvia toppled over like a tree falling down in the forest and the fight was over at just nine seconds into the opening round.

Mercer never fought in MMA again.

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4

Butterbean vs. Bart Gunn

For some reason, WWE decided to tap into the fight market in 1998 with their own tournament dubbed "Brawl for All" where professional wrestlers would strap on a set of gloves and duke it out in a Toughman competition of sorts. Bart Gunn — a lifetime mid-carder during his wrestling days — ended up as an unlikely winner of the tournament after cruising through his fellow WWE superstars with four straight victories, including three wins by knockout. Following his tournament win, WWE then set up him for a boxing match against the "King of the Four Rounders" — Eric "Butterbean" Esch at WrestleMania XV.

The result saw Gunn get absolutely obliterated by "Butterbean" in just 35-seconds after he plowed through the professional wrestler with a right hand that sent him crashing to the canvas in the opening round.

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3

CM Punk vs. Mickey Gall

Former WWE superstar CM Punk decided to try his hand at mixed martial arts after signing with the UFC in 2014. A lifelong fan of MMA, Punk had dabbled in grappling throughout his wrestling career but he signed on with the UFC with the intention of making his professional debut without any prior fight experience.

Punk trained for over a year while working with a long list of UFC veterans, including former lightweight champion Anthony Pettis and current welterweight champion Tyron Woodley in hopes of getting him ready for a fight against up and coming prospect Mickey Gall.

Punk finally realized his dream to step into the Octagon last September at UFC 203, but walking to the cage was probably the highlight for him that night. Punk was choked out by Gall at 2:14 into the opening round.

To his credit, Punk wasn't deterred by the loss and has promised to make his return to the UFC but he still hasn't been booked for another fight since the bout against Gall.

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2

Randy Couture vs. James Toney

Noted boxer James Toney attended a UFC event back in 2010 and it was there where he approached Dana White about possibly fighting in an event for the promotion. At the time, Toney was 42 years old but still a multi-time, multi-weight class champion as a boxer but if he was going to sign with the UFC, they weren't going to give him a pass in his debut.

Enter UFC Hall of Famer Randy Couture, who accepted the fight with Toney at UFC 118 just a few months later.

While Toney promised a knockout, he barely got the chance to throw any punches before Couture had him down on the mat, looking negate his power on the feet. Couture finally wrapped up a head and arm choke submission to get the win at 3:19 into the first round. It was the only time Toney fought in MMA before returning to boxing for nine more fights including a win just last month in Connecticut.

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1

Muhammad Ali vs. Antonio Inoki

In 1976, boxing icon Muhammad Ali traveled to Japan for a "mixed rules" fight with catch wrestler Antonio Inoki. The fight is regarded as one of the true precursors to mixed martial arts as Ali faced Inoki in the ring for 15 rounds with the result ending in a draw.

The action in the fight was nearly non-existent with many critics calling it a low point in Ali's historic career, but there was still a ton of interest in the event and it remains the most talked about crossover match in combat sports — that is until Mayweather vs. McGregor came along.

The legacy of the fight was so interesting that a book on the subject was published last year by noted MMA journalist Josh Gross that told the entire back story on how the bout came together and the backstage politics between the two camps ahead of the event. It's probably not a fight anyone would watch again, but it's still a huge piece of pop culture history, especially considering the superstars involved with the show.